A brewing device with the option to increase the amount of crema created during the brewing operation is known, for example, from the EP 2 168 465 A1. The brewing device described in there is equipped with a so-called crema valve which is arranged between the brewing unit and the coffee outlet and which limits the outflow of the coffee brewed in the brewing device into the coffee outlet pipe by means of a compression-spring-loaded stopper. Due to the fact that the brewed coffee is pressed under pressure in direction of the stopper, the compression spring—provided the brewing water pressure is sufficiently high—exposes an annular gap through which the brewed coffee can flow into the output pipe. Due to the fact that this annular gap is of limited size turbulences are created as the brewed coffee passes through. This swirling through of the brewed coffee causes a fine-pored foam to be created which is called crema.
In order to be able to increase the quantity of crema produced in this way, the conventional brewing device comprises a gas injector with which gas at variable pressure and in variable amounts can be introduced into the crema chamber. Due to this additional swirling through of the coffee within the crema chamber, i.e. after passing through the annular gap, the amount of crema produced in the conventional brewing device is increased. Therefore, whilst it is possible by means of the conventional brewing device to artificially increase the amount of the classically produced crema by introducing a gas into the crema chamber, no provision is made for decreasing the amount of the particular produced crema to a minimum.
Moreover due to the regionally very different coffee cultures and the resulting different drinks of coffee such as Cappuccino, Latte Macchiato, Espresso, different personal tastes exist, wherein there is also a desire as regards the amount and the pore size of the crema to produce less or larger-pore crema, going as far as coffee beverages to be output by the brewing device, which have no crema layer whatsoever.
Due to the use of a compression-spring-loaded valve in the conventional brewing device there is also a danger for drink residues to accumulate in the valve so that this compression-spring-loaded valve gets clogged up to an extent where a smooth operation of the valve is impaired. A compression-spring-loaded valve may under certain circumstances resist the increased pressure of the brewing water before it exposes the annular gap for the passage of the brewed coffee beverage. Whilst this may cause a change in the consistency of the crema, such clogging up in the worst case leads to the valve suddenly releasing under sufficiently high brewing water pressure and explosively opening against the restoring force of the spring. Due to the equally sudden emergence of the coffee in the coffee spout it may therefore happen for example that the coffee sprays out of the spout under excessively initial pressure, resulting in an unsatisfactory coffee beverage.
A further disadvantage of the conventional brewing device consists in that due to the spring-loaded crema valve during standstill of the brewing device, i.e. for example following a completed brewing operation, any coffee water remaining in the coffee outlet pipe builds up behind the crema valve and cannot return into the brewing chamber. When subsequently another brewing operation is performed this residual liquid is initially output at the coffee outlet before the freshly brewed coffee reaches the coffee outlet. In case of a prolonged standstill between consecutive brewing operations it is then possible that this residual liquid has cooled down to such an extent that this has a negative effect upon the temperature of the output coffee beverage.